1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
An image forming apparatus such as a laser beam printer includes a photosensitive drum as an image bearing member, a transfer roller as a transfer unit, and a cleaning blade as a cleaning unit. At the time of performing an image forming operation, a predetermined transfer voltage is applied to the transfer roller in order to transfer a toner as a developer on the photosensitive drum to a recording medium such as paper.
There is known such a configuration that, when the image forming operation is stopped halfway due to a generation of a paper jam or the like, a recovery operation is performed before resuming the image forming operation, to thereby remove the toner remaining on the photosensitive drum without being transferred to the recording medium. The removal of the toner remaining without being transferred is performed by conveying the toner adhered on the photosensitive drum to the cleaning blade along with rotation of the photosensitive drum. At this time, if a voltage having the same polarity as that of the voltage applied in the image forming operation is applied to the transfer roller, the toner on the photosensitive drum is transferred to the transfer roller, and contaminates the transfer roller. Thus, an image defect may occur in the next image formation.
To cope with this problem, Japanese Patent Application Laid-Open No. H04-163560 discloses a configuration for suppressing contamination of the transfer roller due to transfer of the toner on the photosensitive drum to the transfer roller by applying, in the recovery operation, a voltage having a polarity opposite to that of the voltage applied in the image forming operation to the transfer roller.
However, with the method disclosed in Japanese Patent Application Laid-Open No. H04-163560, when the recovery operation is performed in response to the stop of the image forming operation occurring in a state in which a large amount of toner is adhered to the photosensitive drum, a large amount of toner is conveyed to the cleaning blade, and hence the toner may not be completely removed by the cleaning blade. In such a case, the toner that cannot be completely removed and slips through the cleaning blade is adhered to the charging roller, causing a charging failure, which may generate a defective image such as a streaky image. In addition, the toner that has slipped through the cleaning blade may be printed in the next image formation after the recovery operation, causing an image defect such as a streak on an image.